Dynegy's Moss Landing Coal Fired Plant, at Moss Landing Harbor, California, Image credit:NOAACalera has a chemical process in mind to sequester coal-plant C02 emissions in concrete. First, they would bubble hot, CO2-laden stack gas through sea water. The prototype would be done at the pictured Moss Landing plant. Calcium sulfate, and to a lesser extent magnesium sulfate, both of which are present at very low concentration in sea water, will react with the dissolved C02 that results, producing a precipitate of finely divided calcium carbonate (commonly called 'limestone'), plus, perhaps, some dissolved hydrogen sulfide. Read on to see what comes next.Discharged sea water, with byproduct H2S presumably in tow, would be pumped back to the sea.

Next steps: filter or settle out the calcium carbonate particles, rinse out the salt and dry, then blend the dry calcium carbonate with cement for commercial concrete making.

To pull this off, Calera first will have to convince building code standard writers, and, on the way, the Portland Cement Association that it is OK to add a certain percent of this finely divided calcium carbonate to concrete.

Not for the "fly-over states".A power plant using this technology must have direct ocean water access via pipeline, preferably via existing intake/discharge system to avoid capital cost of installing a new one. So, it would be effective only for coastal cities with coal-fired power plants already using sea water for turbine discharge condensation.

A public hearing might be required for the intake/discharge permit. Utility owners would be thrilled at the prospect.

Assuming functionality is a wash, whichever concrete amendment is cheapest to make and ship wins. With millions of tons of fly ash already out there waiting for a market, calcium carbonate produced this way will likely be cost-effective as a concrete additive only if carbon offset credits can be sold. Which, I'd have to guess, might be part of the the strategy.

Shipping finely divided calcium carbonate inland by rail or truck, to places where concrete is made, has a carbon dioxide emission footprint of its own.